Wave separator

ABSTRACT

A wave separator includes an n number (n being a natural number of 3 or larger) of band pass filters having an n number or larger of mutually different pass bands, and a common terminal. For a first of the band pass filters that is one of a band pass filter having a center frequency of a pass band at a lowest side and a band pass filter having a center frequency of a pass band at a highest side and that has a larger or equal difference in a center frequency of a pass band from an adjacent band pass filter as compared with the other band pass filter satisfies a predetermined configuration for a second band pass filter having a pass band adjacent to the first band pass filter.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a wave separator.

2. Description of the Related Art

In recent years, a cellular phone is requested to comply with aplurality of frequency bands and a plurality of wireless systems, orso-called multi-band and multi-mode by a single terminal alone.Therefore, as a module compliant with the multi-band and multi-module,there is suggested a configuration including two duplexers havingdifferent frequency bands, respective antenna terminals of the twoduplexers being connected to a common antenna terminal of the module(for example, see Japanese Unexamined Patent Application Publication No.2010-45563).

However, with the above-described configuration, impedance matching(matching) is optimized on a duplexer-specific basis, i.e.,duplexer-by-duplexer. If the antenna terminals of the duplexers areconnected to the common antenna terminal to configure a multiplexer or awave separator, it is difficult to obtain good impedance matching.Hence, with such a configuration, bandpass loss and return loss may beincreased.

SUMMARY OF THE INVENTION

Accordingly, preferred embodiments of the present invention provide waveseparators that decrease bandpass loss and return loss.

According to a preferred embodiment of the present invention, a waveseparator includes an n number (n being a natural number of 3 or larger)of band pass filters having an n number or larger of mutually differentpass bands; and a common terminal commonly provided for the n number ofband pass filters. Among the n number of band pass filters, for a firstband pass filter that is one of a band pass filter having a centerfrequency of a pass band at a lowest side and a band pass filter havinga center frequency of a pass band at a highest side and that has alarger or equal difference in a center frequency of a pass band from anadjacent band pass filter as compared with the other band pass filter,when f(1) is a center frequency of a pass band and B(1) is a susceptancevalue with the center frequency viewed from the common terminal, andamong the n number of band pass filters, for a second band pass filterhaving a pass band adjacent to the first band pass filter, when f(2) isa center frequency of a pass band and B(2) is a susceptance value withthe center frequency viewed from the common terminal, the first bandpass filter satisfies one of a configuration (i) and a configuration(ii) for the second band pass filter as follows:

(i) B(2)×{2×f(2)−f(1)}/f(1)<B(1)<B(2) if the first band pass filter isthe band pass filter at the highest side, and

(ii) B(2)<B(1)<B(2)×{2×f(2)−f(1)}/f(1) if the first band pass filter isthe band pass filter at the lowest side.

With such a configuration, good impedance matching is obtained for eachof the first band pass filter and the second band pass filter having thepass band adjacent to the first band pass filter by the common matchingcircuit. Accordingly, the bandpass loss and return loss are decreased.

Also, among the n number of band pass filters, for a k-th (2≤k≤n) bandpass filter, when f(k) is a center frequency of a pass band, and B(k) isa susceptance value with the center frequency viewed from the commonterminal, the first band pass filter may satisfy one of a configuration(iii) and a configuration (iv) for each of the second to n-th band passfilters as follows:

(iii) B(k)×{2×f(k)−f(1)}/f(1)<B(1)<B(k) if the first band pass filter isthe band pass filter at the highest side, and

(iv) B(k)<B(1)<B(k)×{2×f(k)−f(1)}/f(1) if the first band pass filter isthe band pass filter at the lowest side.

With such a configuration, good impedance matching is obtained for eachof the first to n-th band pass filters by the common matching circuit.Accordingly, the bandpass loss and return loss are further decreased.

Also, the first band pass filter may be an elastic wave filter includinga series arm resonator connected to the common terminal.

As described above, by providing the series arm resonator connected tothe common terminal, flexibility in design of matching is increased. Tobe specific, by adjusting the number of pairs of electrode fingers ofIDT electrodes of the series arm resonator, the series capacitancecomponent of the first band pass filter is able to be adjusted, andhence the first band pass filter satisfying one of the above-describedconfiguration (i) and configuration (ii) is easily fabricated.

Also, the first band pass filter may further include a parallel armresonator connected between one of nodes of the series arm resonator anda reference terminal.

Herein, in general, with an elastic wave filter, the attenuation in apass band and the characteristics of a suppression band may vary whenthe capacitance component of the series arm resonator is changed. Thus,by providing the parallel arm resonator, the matching and attenuationare stabilized.

Also, the wave separator may further include a matching circuitconnected to the common terminal, and the first band pass filter maysatisfy one of the configuration (i) and the configuration (ii) for thesecond band pass filter without matching by the matching circuit.

Accordingly, the bandpass loss and return loss are decreased without anexternally provided matching circuit.

Also, the matching circuit may be an inductor having one end connectedto the common terminal and the other end connected to the referenceterminal, the inductor may be embedded in a multilayer substrate, andthe n number of band pass filters may be mounted on the multilayersubstrate.

Accordingly, the size is reduced and the bandpass loss and return lossare decreased.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general configuration diagram of a multiplexer according toa first preferred embodiment of the present invention.

FIG. 2 provides a plan view and a cross-sectional view schematicallyshowing a resonator of a surface acoustic wave filter according to thefirst preferred embodiment of the present invention.

FIG. 3 is a general configuration diagram of the multiplexer showing acircuit configuration of a band pass filter according to the firstpreferred embodiment of the present invention.

FIG. 4 provides an illustration for describing a problem occurring whena common matching circuit is connected to a typical multiplexer.

FIG. 5A provides an illustration for describing an example of aconfiguration discovered by the inventors according to the firstpreferred embodiment of the present invention.

FIG. 5B provides an illustration for describing other example of theconfiguration discovered by the inventors according to the firstpreferred embodiment of the present invention.

FIG. 6 is a general configuration diagram of a multiplexer according toa comparative example of the first preferred embodiment.

FIG. 7A is a Smith chart showing impedance in a transmission pass bandof Band4 of a multiplexer according to an example of a preferredembodiment of the present invention.

FIG. 7B is a Smith chart showing impedance in the transmission pass bandof Band4 of a multiplexer according to a comparative example.

FIG. 8A is a Smith chart showing impedance in a transmission pass bandof Band2 of the multiplexer according to the example of a preferredembodiment of the present invention.

FIG. 8B is a Smith chart showing impedance in the transmission pass bandof Band2 of the multiplexer according to the comparative example.

FIG. 9A is a Smith chart showing impedance in a reception pass band ofBand2 of the multiplexer according to the example of a preferredembodiment of the present invention.

FIG. 9B is a Smith chart showing impedance in the reception pass band ofBand2 of the multiplexer according to the comparative example.

FIG. 10A is a Smith chart showing impedance in a reception pass band ofBand4 of the multiplexer according to the example of a preferredembodiment of the present invention.

FIG. 10B is a Smith chart showing impedance in the reception pass bandof Band4 of the multiplexer according to the comparative example.

FIG. 11 is a graph showing the voltage standing wave ratios (VSWR) atthe common terminal side of the multiplexers according to the exampleand comparative example.

FIG. 12 is a general configuration diagram of a multiplexer according toa modification of the first preferred embodiment of the presentinvention.

FIG. 13 is a perspective view of an example of an outer appearance of amultiplexer according to a second preferred embodiment of the presentinvention.

FIG. 14 is an illustration conceptually showing an example of across-sectional structure of the multiplexer according to the secondpreferred embodiment of the present invention.

FIG. 15 is a general configuration diagram of a wave separator accordingto another preferred embodiment of the present invention.

FIG. 16 is a flowchart showing a method of manufacturing a waveseparator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention are described below indetail with reference to the drawings. Any of the preferred embodimentsdescribed below provides a comprehensive or specific example. Numericalvalues, shapes, materials, components, arrangement and connection formof the components, a manufacturing method, and the order in themanufacturing method, etc., described in the following preferredembodiments are merely examples, and are not intended to limit thepresent invention. Elements and features not recited in the independentclaim among elements and features described in the following preferredembodiments are arbitrary components. Also, the sizes and the ratio ofsizes of components shown in the drawings are not necessarily requiredor limiting. Also, in the following preferred embodiments, an expression“be connected to” includes not only direct connection, but also electricconnection through other elements or the like.

Also, in the following preferred embodiments, a multiplexer is describedas an example of a wave separator including an n number (n being anatural number of 3 or larger) of band pass filters having an n numberor larger of mutually different pass bands, and a common terminalcommonly provided for the n number of band pass filters.

First Preferred Embodiment

A multiplexer according to this preferred embodiment includes an nnumber (n being a natural number of 3 or larger) of band pass filtershaving an n number or larger of mutually different pass bands, and acommon terminal commonly provided for the n number of band pass filters.

FIG. 1 is a general configuration diagram of a multiplexer 1 accordingto this preferred embodiment. The drawing also shows an antenna 2 and aninductor 3 connected to a common terminal 21 of the multiplexer 1.

As shown in the drawing, in this preferred embodiment, the multiplexer 1preferably includes four band pass filters 10 to 40 having four mutuallydifferent pass bands, and the common terminal 21. The multiplexer 1 is,for example, a quadplexer that is applied to Band2 (transmission passband: 1850 MHz to 1910 MHz, reception pass band: 1930 MHz to 1990 MHz)and Band4 (transmission pass band: 1710 MHz to 1755 MHz, reception passband: 2110 MHz to 2155 MHz).

The band pass filter 10 is an unbalanced input-unbalanced outputtransmission filter that filters a transmission wave generated by atransmission circuit (radio frequency integrated circuit (RFIC) or thelike) and input from a transmission input terminal 11 in thetransmission pass band of Band4 (1710 MHz to 1755 MHz) and outputs thefiltered transmission wave to the common terminal 21.

A band pass filter 20 is an unbalanced input-unbalanced outputtransmission filter that filters a transmission wave generated by atransmission circuit (RFIC or the like) and input from a transmissioninput terminal 12 in the transmission pass band of Band2 (1850 to 1910MHz) and outputs the filtered transmission wave to the common terminal21.

The band pass filter 30 is an unbalanced input-unbalanced outputreception filter that filters a reception wave input from the commonterminal 21 in the reception pass band of Band2 (1930 MHz to 1990 MHz)and outputs the filtered reception wave to a reception output terminal13.

The band pass filter 40 is an unbalanced input-unbalanced outputreception filter that filters a reception wave input from the commonterminal 21 in the reception pass band of Band4 (2110 MHz to 2155 MHz)and outputs the filtered reception wave to a reception output terminal14.

In this preferred embodiment, the band pass filters 10 to 40 includesurface acoustic wave filters using a surface acoustic wave (SAW). Theconfigurations of the band pass filters 10 to 40 each are not limited tothe elastic wave filter using SAW, and may include an elastic wavefilter using a bulk acoustic wave (BAW). Also, without limiting to theelastic wave filter, a filter including a chip inductor and a chipcapacitor may be used.

A structure of a resonator defining a surface acoustic wave filter willnow be described.

FIG. 2 provides a plan view and a cross-sectional view schematicallyshowing a resonator of a surface acoustic wave filter according to thispreferred embodiment. The drawing exemplarily provides a schematic planview and a schematic cross-sectional view showing a structure of aseries arm resonator 141 (see FIG. 3, described later) among a pluralityof resonators of the band pass filter 40. It is to be noted that theseries arm resonator 141 shown in FIG. 2 is for describing a typicalstructure of the plurality of resonators, and hence the number of pairsand length of electrode fingers defining an electrode are not limited tothose shown in FIG. 2.

The resonators of the band pass filters 10 to 40 each include apiezoelectric substrate 421, and interdigital transducer (IDT)electrodes 411 a and 411 b each having a substantially comb shape.

As shown in the plan view in FIG. 2, a pair of mutually facing IDTelectrodes 411 a and 411 b are located on the piezoelectric substrate421. The IDT electrode 411 a includes a plurality of electrode fingers412 a being parallel or substantially parallel to each other, and abusbar electrode 413 a connecting the plurality of electrode fingers 412a. The IDT electrode 411 b includes a plurality of electrode fingers 412b being parallel or substantially parallel to each other, and a busbarelectrode 413 b connecting the plurality of electrode fingers 412 b. Theplurality of electrode fingers 412 a and 412 b extend in a directionperpendicular or substantially perpendicular to the X-axis direction.

Also, the IDT electrodes 411 a and 411 b including the plurality ofelectrode fingers 412 a and 412 b and the busbar electrodes 413 a and413 b have a multilayer structure including a close contact layer 422and a main electrode layer 423 as shown in the cross-sectional view inFIG. 2.

The close contact layer 422 is a layer that increases adhesion betweenthe piezoelectric substrate 421 and the main electrode layer 423, anduses, for example, Ti as a material. The main electrode layer 423preferably uses, for example, Al containing Cu by 1% as a material.

The materials defining the close contact layer 422 and the mainelectrode layer 423 are not limited to the above-described materials.Further, the IDT electrodes 411 a and 411 b may not have theaforementioned multilayer structure. The IDT electrodes 411 a and 411 bmay be made of, for example, a metal or an alloy selected from Ti, Al,Cu, Pt, Au, Ag, and Pd, or may be defined by a plurality of multilayerbodies made of the above metal or alloy. Also, a dielectric film may belocated on the piezoelectric substrate 421 to cover the close contactlayer 422 and the main electrode layer 423 to protect the electrodes orimprove the characteristics.

The characteristics of the surface acoustic wave filter including theresonator such as the series arm resonator depend on the structure ofthe IDT electrodes of the resonator. Thus, for example, by adjusting thestructure of the IDT electrodes, the band pass filters 10 to 40compliant with the required specifications of the bandpasscharacteristics in respective frequency bands (Bands) are provided.

The structure of the IDT electrodes will now be described.

The wave length of the surface acoustic wave resonator is determined bya repetition pitch λ of the plurality of electrode fingers 412 a and 412b of the IDT electrodes 411 a and 411 b shown in the middle section inFIG. 2. Also, an intersecting width H of the IDT electrodes is a lengthof electrode fingers by which the electrode fingers 412 a of the IDTelectrode 411 a overlap the electrode fingers 412 b of the IDT electrode411 b when viewed in the X-axis direction as shown in the upper sectionin FIG. 2. The X-axis direction extends parallel or substantiallyparallel to a propagation direction of a surface acoustic wave in alongitudinal mode excited at the piezoelectric substrate 421 by the IDTelectrodes. Also, a duty ratio is a line width occupying percentage ofthe plurality of electrode fingers 412 a and 412 b, and is a ratio of aline width of the plurality of electrode fingers 412 a and 412 b to thesum of the line width and a space width of the plurality of electrodefingers 412 a and 412 b. To be more specific, the duty ratio is definedby W/(W+S) when W is a line width of each of the electrode fingers 412 aand 412 b of the IDT electrodes 411 a and 411 b, and S is a space widthbetween adjacent electrode finger 412 a and electrode finger 412 b.

Next, configurations of the band pass filters 10 to 40 are described onthe basis of, for example, the band pass filter 40.

FIG. 3 is a general configuration diagram of the multiplexer 1 showingthe circuit configuration of the band pass filter 40 according to thispreferred embodiment.

As shown in the drawing, the band pass filter 40 includes series armresonators 141 and 143, a parallel arm resonator 142, and alongitudinally coupled type filter portion 144.

The series arm resonators 141 and 143 are connected in series betweenthe common terminal 21 and the reception output terminal 14. Theparallel arm resonator 142 is provided between a connection node of theseries arm resonator 141 and the series arm resonator 143, and areference terminal (ground). The series arm resonators 141 and 143, andthe parallel arm resonator 142 connected as described above configure aladder type band pass filter. The longitudinally coupled type filterportion 144 is provided between the series arm resonator 143 and thereception output terminal 14.

The circuit configuration of the band pass filter 40 is not limited tosuch a configuration, and may be any configuration that can satisfy therequired specifications of the bandpass characteristics in the receptionpass band of Band4. However, to ensure flexibility in design ofimpedance, the series arm resonator and the parallel arm resonator arepreferably provided at the common terminal 21 side. That is, the bandpass filter 40 preferably includes a series arm resonator or a parallelarm resonator connected to the common terminal 21 without other elementinterposed therebetween.

Also, for a specific circuit configuration of each of the band passfilters 10 to 30, a known arrangement configuration may be properlyapplied as long as the configuration can satisfy the requiredspecifications of the bandpass characteristics in each frequency band.The arrangement configuration is, for example, the arranged number ofthe series arm resonators and parallel arm resonators, and selection ofa filter configuration such as ladder type or longitudinally coupledtype.

This preferred embodiment has a feature that a band pass filter havingthe farthest center frequency of a pass band satisfies a predeterminedconfiguration described below in detail to decrease bandpass loss andreturn loss. To be more specific, since the multiplexer 1 according tothis preferred embodiment is applied to Band2 and Band4, the band passfilter 40 being the reception filter of Band4 is the band pass filterhaving the farthest center frequency of the pass band. Hence, the bandpass filter 40 is designed to satisfy the predetermined configuration.

Hereinafter, the circumstances in which the inventors developedpreferred embodiments of the present invention for the configurationsatisfied by the band pass filter having the farthest center frequencyof the pass band is described below.

FIG. 4 provides illustrations for describing a problem occurring when acommon matching circuit is connected to a typical multiplexer. To bespecific, the upper section of the drawing provides a configuration of amultiplexer according to a comparative example. Also, the lower sectionin the drawing provides an admittance chart indicative of an impedanceviewed from a common terminal 921 without a common matching circuitconnected according to the comparative example (not connected tomatching circuit (Lp) in the drawing), and an impedance viewed from thecommon terminal 921 with the common matching circuit connected(connected to matching circuit (Lp) in the drawing).

The multiplexer according to the comparative example has three or moreband pass filters having three or more mutually different pass bands.However, the drawing shows a band pass filter 910 having a pass band ofa first pass band (BPF91) and a band pass filter 940 having a pass bandof a second pass band (BPF94).

These band pass filters 910 and 940 are commonly connected to a commonterminal 921 and an inductor 903 being a common matching circuit. Inthis case, the inductor 903 is a so-called parallel inductor having oneend connected to the common terminal 921 and the other end connected tothe ground.

As shown in the drawing, since the inductor 903 serving as the matchingcircuit is connected, the impedances of the band pass filters 910 and940 move to inductance on an equiconductance circle. That is, since theinductor 903 is connected, the susceptance values of the band passfilters 910 and 940 are decreased.

A variation ΔB in the susceptance value at this time is expressed by1/(2πfLp) when Lp is an inductance value of the inductor 903 and f is acenter frequency of a pass band.

As described above, since the variation ΔB in the susceptance valuedepends on the frequency, the following problem arises between the bandpass filter 910 and the band pass filter 940 having equivalentimpedances without the matching circuit connected. That is, if one ofthe impedances is adjusted to match the characteristic impedance of, forexample, about 50Ω, the other impedance is deviated from thecharacteristic impedance, and hence impedance mismatching may occur.

Such impedance mismatching is particularly noticeable in a filter havinga pass band far from the other filters because the variation ΔB in thesusceptance value depends on the frequency.

Therefore, the inventors discovered that the impedance mismatching ofthe band pass filter is decreased by setting the susceptance value ofthe band pass filter having the farthest pass band within apredetermined range in the multiplexer provided with the parallelinductor as the common matching circuit, and conceived of theconfiguration described below.

Hereinafter, the configuration that decreases the impedance mismatching,discovered and conceived of by the inventors, is described.

FIGS. 5A and 5B are illustrations for describing the configurationdiscovered and conceived of by the inventors. To be specific, FIG. 5A isan illustration for describing a configuration to be satisfied if theband pass filter having the farthest pass band is a band pass filter ata highest side. FIG. 5B is an illustration for describing aconfiguration to be satisfied if the band pass filter having thefarthest pass band is a band pass filter at a lowest side. Also, in eachof FIGS. 5A and 5B, pass bands of four band pass filters (hereinafter,BPF1 to BPF4) are schematically shown in the upper section, and anadmittance chart for describing the range of the susceptance value isshown in the lower section.

The pass bands of BPF1 to BPF4 and the center frequencies (f(1) to f(4))of the pass bands shown in FIG. 5A and the pass bands of BPF1 to BPF4and the center frequencies (f(1) to f(4)) of the pass bands shown inFIG. 5B have different magnitude relationships of frequency forsimplifying the description on the configuration (described later).

First, the definition of the filter having the farthest pass band isdescribed with reference to FIGS. 5A and 5B.

In this preferred embodiment, “the filter having the farthest pass band”is, among an n number of band pass filters, a band pass filter that isone of a band pass filter having a center frequency of a pass band at alowest side and a band pass filter having a center frequency of a passband at a highest side and that has a larger or equal difference in acenter frequency of a pass band from an adjacent band pass filter ascompared with the other band pass filter.

That is, in the example shown in FIG. 5A, among the BPF1 to BPF4 (whenthe relationship among the center frequencies of the respective bandpass filters satisfies BPF4<BPF3<BPF2<BPF1), the BPF4 at the lowest sideor the BPF1 at the highest side is a candidate for “the filter havingthe farthest pass band.” Herein, a difference f(1)−f(2) between thecenter frequency f(1) of the BPF1 and the center frequency f(2) of theBPF2 adjacent to the BPF1 is compared with a difference f(3)−f(4)between the center frequency f(4) of the BPF4 and the center frequencyf(3) of the BPF3 adjacent to the BPF4. Consequently, if a condition(f(1)−f(2)) (f(3)−f(4)) is satisfied, the BPF1 at the highest side isdefined as the band pass filter having the farthest pass band.

Also, in the example shown in FIG. 5B, among the BPF1 to BPF4 (when therelationship among the center frequencies of the respective band passfilters satisfies BPF1<BPF2<BPF3<BPF4), the BPF1 at the lowest side orthe BPF4 at the highest side is a candidate for “the filter having thefarthest pass band.” Herein, a difference f(4)−f(3) between the centerfrequency f(4) of the BPF4 and the center frequency f(3) of the BPF3adjacent to the BPF4 is compared with a difference f(2)−f(1) between thecenter frequency f(1) of the BPF1 and the center frequency f(2) of theBPF2 adjacent to the BPF1. Consequently, if a condition (f(2)−f(1))(f(4)−f(3)) is satisfied, the BPF1 at the lowest side is defined as theband pass filter having the farthest pass band.

In the following description, among the n number of band pass filters,the band pass filter having the farthest pass band defined as describedabove defines and functions as a first band pass filter, and then bandpass filters having pass bands adjacent to the first band pass filterare sequentially described as k-th band pass filters (2≤k≤n).

Also, a configuration in which a matching circuit of a multiplexer iscommonly provided for an n number of band pass filters is expected anddescribed below, and in particular, a configuration to which a parallelinductor is applied as the matching circuit is expected and describedbelow. In the following description, an impedance represents animpedance in a view of a multiplexer side from a common terminal unlessotherwise noted.

First, a predetermined configuration for decreasing bandpass loss andreturn loss if the band pass filter having the farthest pass band (thefirst band pass filter) is a band pass filter at the highest side willbe described.

If a parallel inductor is used as a matching circuit, a variation ΔB(1)in a susceptance (an imaginary part of an admittance) of the first bandpass filter by the provision of the parallel inductor is expressed asfollows:

|ΔB(1)|=1/{2πf(1)Lp}  Expression (1),

where f(1) is a center frequency of a pass band of the first band passfilter, and Lp is an inductance value of the parallel inductor providedas the matching circuit common to the n number of band pass filters.

In a view from the common terminal, to optimize matching of the firstband pass filter, it is the most preferable that the susceptance valuewith the matching circuit is 0. Hence, an optimal value B(1_best) of thesusceptance value of the first band pass filter without the matchingcircuit is expressed as follows:

B(1_best)=|ΔB(1)|=1/{2πf(1)Lp}  Expression (2).

Similarly, if a parallel inductor is used as a matching circuit, avariation ΔB(2) in a susceptance of a second band pass filter by theprovision of the parallel inductor is expressed as follows:

|ΔB(2)|=1/{2πf(2)Lp}  Expression (3),

where f(2) is a center frequency of a pass band of the second band passfilter.

Even for the second band pass filter, similarly to the first band passfilter, in a view from the common terminal, to optimize matching, it isthe most preferable that the susceptance value with the matching circuitis 0. Hence, an optimal value B(2) of the susceptance value of thesecond band pass filter without the matching circuit is expressed asfollows:

B(2)=|ΔB(2)|=1/{2πf(2)Lp}  Expression (4).

As described above, Lp is an inductance value of the parallel inductorprovided as the common matching circuit.

Hence, by solving Expression (4) for Lp, and substituting Lp toExpression (1), the optimal value B(1_best) of the susceptance value ofthe first band pass filter is expressed as follows by using the optimalvalue B(2) of the susceptance value of the second band pass filter:

B(1_best)={f(2)/f(1)}λB(2)  Expression (5).

Accordingly, by setting the susceptance value of the first band passfilter at {f(2)/f(1)}×B(2) without the matching circuit, the followingadvantageous effect is attained. That is, optimal matching is obtainedby the parallel inductor being the common matching circuit, for each ofthe first band pass filter having the greatest difficulty in matchingand the second band pass filter.

Herein, since the center frequencies of the pass bands of the first andsecond band pass filters satisfy the condition of f(1)>f(2), thevariations in the susceptances by the provision of the parallel inductorsatisfy the condition of |ΔB(1)|<|ΔB(2)|.

Accordingly, to decrease the degree of mismatching in the state with thematching circuit, the susceptance value of the first band pass filterwithout the matching circuit is preferably smaller than the optimalvalue B(2) of the susceptance value of the second band pass filter.Hence, a maximum value B(1_max) of the susceptance value of the firstband pass filter without the matching circuit is expressed as follows:

B(1_max)<B(2)  Expression (6).

That is, to decrease the degree of mismatching in the state with thematching circuit, the range of the susceptance value B(1) of the firstband pass filter without the matching circuit is defined in a range ofallowable values smaller than B(2)−B(1_best) with respect to the optimalvalue B(1_best).

Hence, a minimum value B(1_min) of the susceptance value of the firstband pass filter without the matching circuit is expressed as follows:

B(1_min)>B(1_best)−{B(2)−B(1_best)}=2B(1_best)−B(2)=2×{f(2)/f(1)}×B(2)−B(2)=B(2)×{2×f(2)−f(1)}/f(1)  Expression(7).

With regard to Expressions (6) and (7) described above, the inventorsdiscovered that the degree of mismatching is able to be decreased if thefirst band pass filter satisfies a predetermined configuration withoutthe matching circuit. That is, to decrease bandpass loss and returnloss, the inventors conceived of an idea of providing a band pass filteras the band pass filter having the farthest pass band (the first bandpass filter) that satisfies the following configuration for an adjacentband pass filter (the second band pass filter).

That is, among an n number of band pass filters, for a first band passfilter (in this case, BPF1) that is one of a band pass filter having acenter frequency of a pass band at a lowest side and a band pass filterhaving a center frequency of a pass band at a highest side and that hasa larger or equal difference in a center frequency of a pass band froman adjacent band pass filter as compared with the other band passfilter, it is assumed that f(1) is a center frequency of a pass band andB(1) is a susceptance value with the center frequency viewed from acommon terminal in a state without a matching circuit. Also, among the nnumber of band pass filters, for a second band pass filter (in thiscase, BPF2) having a pass band adjacent to the first band pass filter,it is assumed that f(2) is a center frequency of a pass band and B(2) isa susceptance value with the center frequency viewed from the commonterminal in the state without the matching circuit.

At this time, the first band pass filter satisfies a configuration (i)as follows for the second band pass filter:

a configuration (i) B(2)×{2×f(2)−f(1)}/f(1)<B(1)<B(2) if the first bandpass filter is the band pass filter at the highest side.

By providing the first band pass filter satisfying this configuration(i), if the first band pass filter is the band pass filter at thehighest side, good matching is obtained by the common matching circuitfor each of the first band pass filter having the greatest difficulty inmatching, and the second band pass filter.

Herein, “good matching” or “good impedance matching” represents that thevoltage standing wave ratio (VSWR) in each frequency band (Band) issmall, and in this preferred embodiment, represents that the VSWR issmaller than a value corresponding to the required specifications of thebandpass characteristics (for example, smaller than 2.0).

Also, the inventors discovered that, if the first band pass filtersatisfies the following configuration for a k-th (2≤k≤n) band passfilter among the n number of band pass filters, the degree ofmismatching is able to be further decreased.

That is, for the k-th (2≤k≤n) band pass filter among the n number ofband pass filters, it is assumed that f(k) is a center frequency of apass band, and B(k) is a susceptance value with the center frequencyviewed from the common terminal.

At this time, the first band pass filter satisfies a configuration (iii)as follows for each of the second to n-th band pass filters:

a configuration (iii) B(k)×{2×f(k)−f(1)}/f(1)<B(1)<B(k) if the firstband pass filter is the band pass filter at the highest side.

By providing the first band pass filter satisfying this configuration(iii), if the first band pass filter is the band pass filter at thehighest side, good matching is obtained by the common matching circuitfor each of the n number of band pass filters.

Next, a predetermined configuration to decrease bandpass loss and returnloss if the band pass filter having the farthest pass band (the firstband pass filter) is a band pass filter at the lowest side is described.

In the following description, the configuration is similar to the casein which the band pass filter at the highest side is the farthest bandpass filter except for the magnitude relationship of the centerfrequencies of the pass bands of the band pass filters. Hence, thedescription is appropriately simplified or omitted.

The optimal value B(1_best) of the susceptance value of the first bandpass filter is expressed by an expression as follows by using theoptimal value B(2) of the susceptance value of the second band passfilter:

B(1_best)={f(2)/f(1)}×B(2)  Expression (8),

where f(1) is a center frequency of a pass band of the first band passfilter, and f(2) is a center frequency of a pass band of the second bandpass filter.

Herein, the center frequencies of the pass bands of the first and secondband pass filters satisfy a condition of f(1)<f(2). Hence, a variationΔB(1) in the susceptance of the first band pass filter and a variationΔB(2) in the susceptance of the second band pass filter by the provisionof the parallel inductor as the matching circuit satisfy a condition of|ΔB(1)|>|ΔB(2)|.

Accordingly, to decrease the degree of mismatching in the state with thematching circuit, the susceptance value of the first band pass filterwithout the matching circuit is preferably larger than the optimal valueB(2) of the susceptance value of the second band pass filter. Hence, aminimum value B(1_min) of the susceptance value of the first band passfilter without the matching circuit is expressed as follows:

B(1_min)>B(2)  Expression (9).

That is, to decrease the degree of mismatching in the state with thematching circuit, the range of the susceptance value B(1) of the firstband pass filter without the matching circuit is defined in a range ofallowable values smaller than B(1_best)−B(2) with respect to the optimalvalue B(1_best).

Hence, a maximum value B(1_max) of the susceptance value of the firstband pass filter without the matching circuit is expressed as follows:

B(1_max)<B(1_best)+{B(1_best)−B(2)}=2B(1_best)−B(2)=2×{f(2)/f(1)}×B(2)−B(2)=B(2)×{2×f(2)−f(1)}/f(1)  Expression(10).

With regard to Expressions (9) and (10) described above, the inventorsdiscovered that the degree of mismatching is able to be decreased if thefirst band pass filter satisfies a predetermined configuration in thestate without the matching circuit. That is, to decrease bandpass lossand return loss, the inventors conceived of an idea of providing a bandpass filter as the band pass filter having the farthest pass band (thefirst band pass filter) that satisfies the following configuration foran adjacent band pass filter (the second band pass filter).

That is, among an n number of band pass filters, for a first band passfilter (in this case, BPF1) that is one of a band pass filter having acenter frequency of a pass band at a lowest side and a band pass filterhaving a center frequency of a pass band at a highest side and that hasa larger or equal difference in a center frequency of a pass band froman adjacent band pass filter as compared with the other band passfilter, it is assumed that f(1) is a center frequency of a pass band andB(1) is a susceptance value with the center frequency viewed from acommon terminal in a state without a matching circuit. Also, among the nnumber of band pass filters, for a second band pass filter (in thiscase, BPF2) having a pass band adjacent to the first band pass filter,it is assumed that f(2) is a center frequency of a pass band and B(2) isa susceptance value with the center frequency viewed from the commonterminal without the matching circuit.

At this time, the first band pass filter satisfies a configuration (ii)as follows for the second band pass filter:

a configuration (ii) B(2)<B(1)<B(2)×{2×f(2)−f(1)}/f(1) if the first bandpass filter is the band pass filter at the lowest side.

By providing the first band pass filter satisfying this configuration,if the first band pass filter is the band pass filter at the lowestside, good matching is obtained by the common matching circuit for eachof the first band pass filter having the greatest difficulty inmatching, and the second band pass filter.

Also, the inventors discovered that, if the first band pass filtersatisfies the following configuration for a k-th (2≤k≤n) band passfilter among the n number of band pass filters, the degree ofmismatching is able to be further decreased.

That is, for the k-th (2≤k≤n) band pass filter among the n number ofband pass filters, it is assumed that f(k) is a center frequency of apass band, and B(k) is a susceptance value with the center frequencyviewed from the common terminal.

At this time, the first band pass filter satisfies a configuration (iv)as follows for each of the second to n-th band pass filters:

a configuration (iv) B(k)×{2×f(k)−f(1)}/f(1)<B(1)<B(k) if the first bandpass filter is the band pass filter at the lowest side.

By providing the first band pass filter satisfying this configuration(iv), if the first band pass filter is the band pass filter at thelowest side, good matching is obtained by the common matching circuitfor each of the n number of band pass filters.

Next, for characteristics of the multiplexer according to this preferredembodiment, an example of this preferred embodiment is described ascompared with a comparative example.

FIG. 6 is a general configuration diagram of a multiplexer 1A showing acircuit configuration of a band pass filter 40A according to thecomparative example.

The multiplexer 1A according to the comparative example is a quadplexerin which a duplexer for Band2 and a duplexer for Band4 are connected bythe common terminal 21. To be specific, as shown in FIG. 6, thecomparative example is almost similar to the example except for theconfiguration of the band pass filter 40A (reception filter of Band4)having a pass band being the farthest from the other band pass filters.To be more specific, the band pass filter 40A according to thecomparative example does not include the parallel arm resonator 142 orthe series arm resonator 143 as compared with the band pass filter 40according to the example.

Table 1 shows the details of the structure (the intersecting width H,the n number of pairs of electrode fingers of the IDT electrodes) of theseries arm resonators 141 and 143 and the parallel arm resonator 142 ofthe band pass filter 40 according to the example, and the structure of aseries arm resonator 141A of the band pass filter 40A according to thecomparative example. The dimension of the intersecting width H isprovided by micrometer (μm) and wave length ratio that is a multiplierof the wave length λ determined by the pitch of electrode fingers of theIDT electrodes. To be specific, in the IDTs of the series arm resonator141, the intersecting width H is about 33 μm corresponding to about 18.4times the wave length λ, and the number of pairs of electrode fingers is100, for example.

TABLE 1 Example Comparative Series arm Parallel arm Series arm exampleresonator resonator resonator Series arm 141 142 143 resonator 141AIntersecting about 33 about 67 about 30 about 33 width H (μm)Intersecting 18.4 36.6 16.0 18.4 width H (wave length ratio) N Number of100 120 35 80 electrode fingers of IDT electrodes

The pitch λ and the duty ratio D are appropriately determined inaccordance with the required specifications of the bandpasscharacteristics in the reception pass band of Band4. Also, thecapacitance of each resonator is determined by the structure shown inTable 1 and, for example, the dielectric constant of the piezoelectricsubstrate 421.

Herein, in this preferred embodiment, by increasing or decreasing thenumber of pairs of electrode fingers of the IDT electrodes of the seriesarm resonator 141, the band pass filter 40 is formed to satisfy theabove-described configuration (i).

To be specific, the band pass filter 40 includes the series armresonator 141 connected to the common terminal 21. This series armresonator 141 is connected to the common terminal 21 without otherelements interposed therebetween.

With this configuration, by increasing or decreasing the number of pairsof electrode fingers of the IDT electrodes of the series arm resonator141, the capacitance component of the band pass filter 40 viewed fromthe common terminal 21 is able to be increased or decreased, and hencethe susceptance value is able to be adjusted.

The method of adjusting the susceptance value is not limited to theaforementioned method. For example, adjustment may be made byparallel-connecting a capacitor to a resonator of the band pass filter40, or by changing the electrode film thickness or the duty ratio of theresonator.

Also, in this preferred embodiment, the number of pairs of electrodefingers of the IDT electrodes is increased in the series arm resonator141 according to the example as compared with the series arm resonator141A according to the comparative example. The increase in the number ofpairs of electrode fingers of the IDT electrodes in the series armresonator 141 may decrease the attenuation of the band pass filter 40.Thus, in this preferred embodiment, the parallel arm resonator 142 isprovided between one of nodes of the series arm resonator 141 and thereference terminal (ground). Accordingly, the decrease in attenuation isrestricted.

Hereinafter, frequency characteristics of the multiplexer 1 according tothe thus configured example are described in comparison with themultiplexer 1A according to the comparative example.

FIGS. 7A to 10B each are a Smith chart indicative of impedance of themultiplexer viewed from the common terminal 21 in the state with thecommon matching circuit at the common terminal 21 of the multiplexer. Asthe matching circuit according to the example, an inductor 3 with aninductance value of 1.6 nH having one end connected to the commonterminal 21 and the other end connected to the ground was used. Also, asthe matching circuit according to the comparative example, an inductor 3with an inductance value of 1.7 nH having one end connected to thecommon terminal 21 and the other end connected to the ground was used.

To be specific, FIG. 7A shows the impedance of the multiplexer 1according to the example in the transmission pass band of Band4. Also,FIG. 7B shows the impedance of the multiplexer 1A according to thecomparative example in the transmission pass band of Band4. Also, FIG.8A shows the impedance of the multiplexer 1 according to the example inthe transmission pass band of Band2. Also, FIG. 8B shows the impedanceof the multiplexer 1A according to the comparative example in thetransmission pass band of Band2. Also, FIG. 9A shows the impedance ofthe multiplexer 1 according to the example in the reception pass band ofBand2. Also, FIG. 9B shows the impedance of the multiplexer 1A accordingto the comparative example in the reception pass band of Band2. Also,FIG. 10A shows the impedance of the multiplexer 1 according to theexample in the reception pass band of Band4. Also, FIG. 10B shows theimpedance of the multiplexer 1A according to the comparative example inthe reception pass band of Band4.

These drawings each show the locus of the impedance in a band containingfour pass bands (for example, 1500 MHz to 2300 MHz). In each drawing,the locus of the pass band (Band) in the drawing is indicated by a thickline.

As shown in FIGS. 7A to 9B, it is discovered that the multiplexer 1according to the example maintains good impedance matching in thetransmission pass band of Band4 and the transmission and reception passbands of Band2 as compared with the comparative example. That is,according to the example, even if the band pass filter 40 is configuredto satisfy the above-described configuration (i), the impedance matchingof the other band pass filters 10 to 30 is maintained.

Also, as shown in FIGS. 10A and 10B, it is discovered that themultiplexer 1 according to the example has good impedance matching inthe reception pass band of Band4 as compared with the comparativeexample. That is, according to the example, since the band pass filter40 is adjusted to satisfy the above-described configuration (i), theimpedance mismatching of the band pass filter 40 is decreased.

As described above, with the multiplexer 1 according to the example, forthe band pass filter 40 having the farthest pass band among the fourband pass filters 10 to 40, the impedance mismatching of the other bandpass filters 10 to 30 is able to be decreased while the impedancematching is maintained.

To be specific, the multiplexer 1A according to the comparative exampleis configured by connecting a duplexer for Band1 and a duplexer forBand4 through the common terminal 21. Herein, a duplexer is generallyprovided to attain impedance matching by a common matching circuit in astate in which the susceptance of own pass band and one target pass bandare matched to two bands (reception pass band and transmission passband). Hence, impedance mismatching may occur in the multiplexer 1Aconfigured by combining such duplexers.

In contrast, since the band pass filter 40 satisfies the above-describedconfiguration (i), the multiplexer 1 according to the example decreasesthe impedance mismatching.

FIG. 11 is a graph showing the VSWRs at the common terminal 21 side ofthe multiplexers according to the example and comparative example.

As shown in the drawing, it is discovered that the VSWR is degraded inthe reception pass band of Band4 according to the comparative example.This is because good impedance matching cannot be obtained by theconfiguration according to the comparative example as shown in FIG. 10B.

In contrast, it is discovered that the multiplexer 1 according to theexample obtains good VSWR even in the reception pass band of Band4 ascompared with the comparative example. That is, according to theexample, since the band pass filter 40 is provided to satisfy theabove-described configuration (i), the impedance mismatching of the bandpass filter 40 is decreased and hence the VSWR is improved.

Table 2 shows maximum values of VSWR in respective pass bands(transmission pass band of Band4: B4Tx, transmission pass band of Band2:B2Tx, reception pass band of Band2: B2Rx, reception pass band of Band4:B4Rx).

TABLE 2 B4Tx B2Tx B2Rx B4Rx Example 1.27 1.30 1.47 1.71 Comparative 1.311.20 1.56 2.13 example

As shown in this table, according to the example, the VSWR is restrictedto be 2.0 or smaller in all the four bands. Also, in the example, theVSWR of the reception pass band of Band4 is improved while the VSWRs ofbands other than the reception pass band of Band4 are maintained atsubstantially equivalent levels as compared with the comparativeexample.

6. Conclusion

As described above, a multiplexer 1 according to this preferredembodiment includes an n number (n being a natural number of 3 orlarger) of band pass filters having an n number or larger of mutuallydifferent pass bands (in this preferred embodiment, four band passfilters 10 to 40 having four pass bands), and a common terminal 21commonly provided for the n number of band pass filters. Among the nnumber of band pass filters, a first band pass filter that is one of aband pass filter having a center frequency of a pass band at a lowestside and a band pass filter having a center frequency of a pass band ata highest side and that has a larger or equal difference in a centerfrequency of a pass band from an adjacent band pass filter as comparedwith the other band pass filter satisfies one of the above-describedconfiguration (i) and configuration (ii) (in this preferred embodiment,the band pass filter 40 at the highest side satisfies the configuration(i)).

With this configuration, good impedance matching is able to be providedby the common matching circuit such as a parallel inductor (in thispreferred embodiment, the inductor 3) for each of the first band passfilter and the second band pass filter having the pass band adjacent tothe first band pass filter (in this preferred embodiment, the band passfilter 40 and the band pass filter 30). Accordingly, with themultiplexer 1 according to this preferred embodiment, the bandpass lossand return loss are decreased.

In general, in a multiplexer having an n number or larger of pass bands,bandpass loss and return loss are likely increased in a pass band at thehighest side or the lowest side. Since the susceptance value of the bandpass filter at the lowest side or the highest side satisfies one of theabove-described configuration (i) and configuration (ii) and hence goodimpedance matching is provided by the common matching circuit, thebandpass loss and return loss are effectively decreased in the pass bandin which the bandpass loss and return loss are likely increased.

Also, in the multiplexer 1 according to this preferred embodiment, thefirst band pass filter satisfies one of the above-describedconfiguration (iii) and configuration (iv) for each of the second ton-th band pass filters (in this preferred embodiment, the band passfilter 40 at the highest side satisfies the configuration (iii) for theband pass filters 10 to 30).

With this configuration, good impedance matching is provided by thecommon matching circuit such as the parallel inductor for each of thefirst to n-th band pass filters (in this preferred embodiment, the bandpass filters 10 to 40). Accordingly, with the multiplexer 1 according tothis preferred embodiment, the bandpass loss and return loss are furtherdecreased.

Also, with the multiplexer 1 according to this preferred embodiment, thefirst band pass filter (in this preferred embodiment, the band passfilter 40) preferably is an elastic wave filter (in this preferredembodiment, the surface acoustic wave filter) including the series armresonator 141 connected to the common terminal 21.

As described above, by providing the series arm resonator 141 connectedto the common terminal 21, the flexibility in design of matching isincreased. To be specific, by adjusting the number of pairs of electrodefingers of the IDT electrodes of the series arm resonator 141, theseries capacitance component of the first band pass filter (in thispreferred embodiment, the band pass filter 40) is able to be adjusted,and hence the first band pass filter satisfying one of theabove-described configuration (i) and configuration (ii) is able to beeasily fabricated.

Also, in the multiplexer 1 according to this preferred embodiment, theparallel arm resonator 142 is provided between one of the nodes of theseries arm resonator 141 and the reference terminal (ground).

Herein, in general, with an elastic wave filter, the attenuation in apass band and the characteristics of a suppression band may vary if thecapacitance component of the series arm resonator is changed. Thus, inthis preferred embodiment, by providing the parallel arm resonator 142,the variation in characteristics is significantly reduced or prevented.The matching and attenuation are stabilized.

In this preferred embodiment, the multiplexer applied to Band2 and Band4is described as an example of the multiplexer; however, the bands to beapplied are not limited thereto. For example, Band1 (transmission passband: 1920 MHz to 1980 MHz, reception pass band: 2110 MHz to 2170 MHz)and Band3 (transmission pass band: 1710 MHz to 1785 MHz, reception passband: 1805 MHz to 1880 MHz) may be applied.

Also, in the multiplexer, the band pass filter may be the band passfilter at the lowest side having the farthest center frequency of thepass band. In this case, if the band pass filter 40 at the lowest sidesatisfies the above-described configuration (ii) and furtherconfiguration (iv), an advantageous effect similar to that of thispreferred embodiment is attained.

Also, the multiplexer may be applied to a filter having three or morepass bands. FIG. 12 is a general configuration diagram of a multiplexer1B according to a modification of this preferred embodiment. Forexample, as shown in FIG. 12, the multiplexer 1B that handles signals ofBand3 and Band4 preferably defines a triplexer including a band passfilter 10B that executes filtering in transmission pass bands of Band3and Band4, a band pass filter 30B that executes filtering in a receptionband of Band3, and the band pass filter 40 that executes filtering in areception band of Band4.

Also, the conductance (the imaginary part of the admittance) of each ofthe n number of band pass filters (in this preferred embodiment, fourband pass filters 10 to 40) is not particularly limited. However, anormalized conductance is preferably in a range from about 0.7 to about1.4 (inclusive), for example. By setting the normalized conductancewithin this range, the VSWR at the common terminal 21 side of themultiplexer 1 can be set at about 1.7 or smaller, for example.

Second Preferred Embodiment

In the above-described first preferred embodiment, the multiplexer 1preferably is connected to the externally provided matching circuit suchas the inductor 3. However, the multiplexer may include the matchingcircuit. That is, the multiplexer may be a multiplexer having embeddedtherein the matching circuit.

FIG. 13 is a perspective (oblique) view showing an example of an outerappearance of a multiplexer 101 according to this preferred embodiment.FIG. 14 is an illustration conceptually showing an example of across-sectional structure of the multiplexer 101 according to thispreferred embodiment. FIG. 13 shows a sealing resin 60 in a perspective(transparent) manner. Also, FIG. 14 is a side view of the band passfilters 10 to 40.

As shown in FIGS. 13 and 14, the multiplexer 101 includes the band passfilters 10 to 40 configured as, for example, piezoelectric chips, andprovided on one of principal surfaces of a multilayer substrate 50having embedded therein the inductor 3. That is, the band pass filters10 to 40 are mounted on the multilayer substrate 50.

One of an input terminal and an output terminal of each of the band passfilters 10 to 40 is connected to, for example, the common terminal 21defined by a surface electrode of the multilayer substrate 50 by wiringprovided at the multilayer substrate 50. In this preferred embodiment,the band pass filters 10 to 40 are sealed with the sealing resin 60,such as thermosetting resin or photo-curable resin. The material of thesealing resin 60 is not particularly limited as long as the material isan insulating material. Also, the band pass filters 10 to 40 may not besealed with the sealing resin 60.

The multilayer substrate 50 includes various conductors that define theinductor 3 and the circuit of the multiplexer 101. The conductorsinclude a surface electrode to mount the multiplexer 101 on a motherboard such as a printed circuit board, a surface electrode to mount theband pass filters 10 to 40 on the multilayer substrate 50, asubstantially loop-shaped in-plane conductor defining the inductor 3,and an inter-layer conductor that penetrates through respective layersin the thickness direction.

With this preferred embodiment, since the multiplexer 101 includes thematching circuit (in this preferred embodiment, the inductor 3), thebandpass loss and return loss are decreased without an externallyprovided matching circuit.

Also, in this preferred embodiment, since the band pass filters 10 to 40are mounted on the multilayer substrate 50 having embedded therein theinductor 3, the size is reduced and the bandpass loss and return lossare decreased.

Alternatively, the multiplexer having embedded therein the matchingcircuit may include a matching circuit mounted on a printed circuitboard or the like, and band pass filters 10 to 40 mounted on the printedcircuit board.

Other Preferred Embodiments

The multiplexers according to the preferred embodiments and theirmodifications have been described above; however, the present inventionis not limited to the individual preferred embodiments and theirmodifications. Without departing from the scope of the presentinvention, configurations obtained by adding various modificationsconceivable by those skilled in the art to the preferred embodiments andtheir modifications, and preferred embodiments constructed by combiningthe components in the different preferred embodiments and theirmodifications may be included in one aspect or a plurality of aspects ofthe present invention.

Also, in the above description, the multiplexer is exemplified; however,the present invention may be applied to a wave separator including an nnumber (n being a natural number of 3 or larger) of band pass filtershaving an n number or larger of mutually different pass bands, and thecommon terminal commonly provided for the n number of band pass filters.That is, all band pass filters may be reception side filters that filtera reception wave input from the common terminal 21 in a predeterminedreception pass band, and output the filtered reception wave to areception output terminal.

FIG. 15 is a general configuration diagram of a wave separator 201according to another preferred embodiment of the present invention. Thedrawing also shows the antenna 2 and a matching circuit 103 connected toa common terminal 121 of the wave separator 201.

The wave separator 201 shown in the drawing includes three band passfilters 110 to 130 having three mutually different pass bands (Rx1 toRx3). Respective input terminals of the band pass filters 110 to 130 areconnected to the common terminal 121.

Also in this wave separator 201, among the three band pass filters 110to 130, a first band pass filter that is one of a band pass filterhaving a center frequency of a pass band at a lowest side and a bandpass filter having a center frequency of a pass band at a highest sideand that has a larger or equal difference in a center frequency of apass band from an adjacent band pass filter as compared with the otherband pass filter satisfies one of the above-described configuration (i)and configuration (ii), and hence an advantageous effect similar to theabove-described preferred embodiments is attained. That is, the waveseparator 201 is able to decrease the bandpass loss and return loss.

Also, in the above description, the inductor 3 having one end connectedto the common terminal 21 and the other end connected to the ground isdescribed as an example of the matching circuit connected to the commonterminal 21. However, the matching circuit is not limited to thisconfiguration. For example, as shown in FIG. 15, the matching circuitmay include an inductor 103 a having one end connected to the commonterminal 121 and the other end connected to the ground, and a capacitor103 b provided in series between the antenna 2 and the common terminal121.

Also, a preferred embodiment of the present invention may be realized asa method of manufacturing the wave separator. FIG. 16 is a flowchartshowing a method of manufacturing the wave separator.

That is, the method of manufacturing the wave separator is a method ofmanufacturing a wave separator including an n number (n being a naturalnumber of 3 or larger) of band pass filters having an n number or largerof mutually different pass bands and a common terminal commonlyconnected to the n number of band pass filters. Among the n number ofband pass filters, for a first band pass filter that is one of a bandpass filter having a center frequency of a pass band at a lowest sideand a band pass filer having a center frequency of a pass band at ahighest side and that has a larger or equal difference in a centerfrequency of a pass band from an adjacent band pass filter as comparedwith the other band pass filter, when f(1) is a center frequency of apass band and B(1) is a susceptance value with the center frequencyviewed from the common terminal, and among the n number of band passfilters, for a second band pass filter having a pass band adjacent tothe first band pass filter, when f(2) is a center frequency of a passband and B(2) is a susceptance value with the center frequency viewedfrom the common terminal, the method includes a step of forming thesecond band pass filter (S10), and a step of providing the first bandpass filter (S20) so that the first band pass filter satisfies one of aconfiguration (i) and a configuration (ii) for the second band passfilter as follows:

(i) B(2)×{2×f(2)−f(1)}/f(1)<B(1)<B(2) if the first band pass filter isthe band pass filter at the highest side, and

(ii) B(2)<B(1)<B(2)×{2×f(2)−f(1)}/f(1) if the first band pass filter isthe band pass filter at the lowest side.

To be specific, in the step of forming the second band pass filter(S10), each k-th (2≤k≤n) band pass filter among the n number of bandpass filters is designed, and for the k-th (2≤k≤n) band pass filter,when f(k) is a center frequency of a pass band and B(k) is a susceptancevalue with the center frequency viewed from the common terminal, in thestep of forming the first band pass filter, design is made so that thefirst band pass filter satisfies one of a configuration (iii) and aconfiguration (iv) for each of the second to n-th band pass filters asfollows:

(iii) B(k)×{2×f(k)−f(1)}/f(1)<B(1)<B(k) if the first band pass filter isthe band pass filter at the highest side, and

(iv) B(k)<B(1)<B(k)×{2×f(k)−f(1)}/f(1) if the first band pass filter isthe band pass filter at the lowest side.

Also, to be specific, the first band pass filter is an elastic wavefilter having a series arm resonator connected to the common terminal.In the step of forming the first band pass filter (S20), design is madeto satisfy one of the above-described configuration (i) andconfiguration (ii) by increasing or decreasing the number of pairs ofelectrode fingers of the IDT electrodes of the series arm resonator.

Such a method of manufacturing the wave separator is executed by using,for example, a computer such as a computer-aided design (CAD) device.Also, the manufacturing method may be executed by the computer throughan interactive operation by a designer with the computer.

The step of forming the second band pass filter (S10) and the step offorming the first band pass filter (S20) may be executed sequentially inthat order, may be executed in the inverted order, or may be executed atthe same time.

For example, the steps (S10 and S20) may be executed at the same time byusing an automatic tool such as electronic design automation (EDA) withregard to the structure, such as the number of pairs of electrodefingers of the IDT electrodes corresponding to the requiredspecifications of the bandpass characteristics in each frequency band(Band).

Preferred embodiments of the present invention can be widely used as amultiplexer having low bandpass loss and low return loss, for acommunication device such as a cellular phone.

As described above, multiplexers according to preferred embodiments ofthe present invention are not limited to being applied to Band1, Band2,Band3, and/or Band4. For example, a multiplexer according to a preferredembodiment of the present invention may be applied to Band30(transmission pass band: 2305 MHz to 2315 MHz, reception pass band: 2350MHz to 2360 MHz). As another example, a multiplexer according to apreferred embodiment of the present invention may be applied to Band1(transmission pass band: 2500 MHz to 2570 MHz, reception pass band: 2620MHz to 2690 MHz).

Further, the multiplexers according to preferred embodiments of thepresent invention are not limited to being a triplexer or a quadplexer.As described above, the multiplexer may include an n number of band passfilters (n being a natural number of 3 or larger). For example, amultiplexer according to a preferred embodiment of the present inventionmay be a hexplexer (six-band multiplexer).

A multiplexer according to a preferred embodiment of the presentinvention is a hexplexer that is applied to Band2 (transmission passband B2Tx: 1850 MHz to 1910 MHz, reception pass band B2Rx: 1930 MHz to1990 MHz), Band4 (transmission pass band B4Tx: 1710 MHz to 1755 MHz,reception pass band B4Rx: 2110 MHz to 2155 MHz), and Band30(transmission pass band B30Tx: 2305 MHz to 2315 MHz, reception pass bandB30Rx: 2350 MHz to 2360 MHz). That is, in the present preferredembodiment, the multiplexer preferably includes a common terminal andsix band pass filters having six mutually different pass bands B4Tx,B2Tx, B2Rx, B4Rx, B30Tx, and B30Rx. Preferably, the multiplexerincludes, but is not limited to, components that are similar orsubstantially similar to those of the multiplexer according to the firstpreferred embodiment, and additionally includes a fifth band pass filterthat executes filtering in the transmission band of Band30 and a sixthband pass filter that executes filtering in the reception band ofBand30. Preferably, the fifth band pass filter is an unbalancedinput-unbalanced output transmission filter, for example, that filters atransmission wave generated by a transmission circuit (RFIC or othersuitable transmission circuit) and input from a transmission inputterminal in the transmission pass band of Band30 and outputs thefiltered transmission wave to the common terminal. The configuration ofthe fifth band pass filter in the present preferred embodiment mayinclude, but is not limited to, any structure or circuit configurationas described above, or any configuration that is able to satisfy therequired specifications of the bandpass characteristics in thetransmission pass band of Band30.

Preferably, the sixth band pass filter is an unbalanced input-unbalancedoutput reception filter that filters a reception wave input from thecommon terminal in the reception pass band of Band30 and outputs thefiltered reception wave to a reception output terminal. Theconfiguration of the sixth band pass filter in the present preferredembodiment may include, but is not limited to, any structure or circuitconfiguration as described above, or any configuration that is able tosatisfy the required specifications of the bandpass characteristics inthe reception pass band of Band30. Also, in this multiplexer, one ormore of the above-described configurations (i), (ii), (iii), and (iv)may be applied, and advantageous effects similar to those of the firstpreferred embodiment are attained.

In another preferred embodiment of the present invention, themultiplexer is a hexplexer that is applied to Band1 (transmission passband B1Tx: 1920 MHz to 1980 MHz, reception pass band B1Rx: 2110 MHz to2170 MHz), Band3 (transmission pass band B3Tx: 1710 MHz to 1785 MHz,reception pass band B3Rx: 1805 MHz to 1880 MHz), and Band1 (transmissionpass band B7Tx: 2500 MHz to 2570 MHz, reception pass band B7Rx: 2620 MHzto 2690 MHz). In the present preferred embodiment, the multiplexerpreferably includes a common terminal and six band pass filters havingsix mutually different pass bands B3Tx, B3Rx, B1Tx, B1Rx, B7Tx, andB7Rx. The configuration of each of the six band pass filters in thepresent preferred embodiment may include, but is not limited to, any ofthe structures or circuit configurations as described above, or anyconfiguration that is able to satisfy the required specifications of thebandpass characteristics in the respective bands B3Tx, B3Rx, B1Tx, B1Rx,B7Tx, and B7Rx. Also, in this multiplexer, one or more of theabove-described configurations (i), (ii), (iii), and (iv) may beapplied, and advantageous effects similar to those of the firstpreferred embodiment are attained.

Further, as described above, the multiplexer according to the firstpreferred embodiment of the present invention may be applied to Band1and Band3, instead of Band2 and Band4. For example, a multiplexeraccording to another preferred embodiment of the present invention is aquadplexer that is applied to Band1 (transmission pass band B1Tx: 1920MHz to 1980 MHz, reception pass band B1Rx: 2110 MHz to 2170 MHz) andBand3 (transmission pass band B3Tx: 1710 MHz to 1785 MHz, reception passband B3Rx: 1805 MHz to 1880 MHz). In the present preferred embodiment,the multiplexer preferably includes a common terminal and four band passfilters having four mutually different pass bands B3Tx, B3Rx, B1Tx, andB1Rx. The configuration of each of the four band pass filters in thepresent preferred embodiment may include, but is not limited to, any ofthe structures or circuit configurations as described above, or anyconfiguration that can satisfy the required specifications of thebandpass characteristics in the respective bands B3Tx, B3Rx, B1Tx, andB1Rx. Also, in this multiplexer, one or more of the above-describedconfigurations (i), (ii), (iii), and (iv) may be applied, andadvantageous effects similar to those of the first preferred embodimentare attained.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A wave separator comprising: an n number of bandpass filters including an n number or larger of mutually different passbands where n is a natural number of 3 or larger; and a common terminalcommonly provided for the n number of band pass filters; wherein atleast one of the n number of band pass filters includes a surfaceacoustic wave filter or a bulk acoustic wave filter; among the n numberof band pass filters, for a first band pass filter that is one of a bandpass filter having a center frequency of a pass band at a lowest sideand a band pass filter having a center frequency of a pass band at ahighest side and that has a larger or equal difference in a centerfrequency of a pass band from an adjacent band pass filter as comparedwith the other of the lowest side band pass filter and the highest sideband pass filter and a band pass filter adjacent thereto, when f(1) is acenter frequency of a pass band and B(1) is a susceptance value with thecenter frequency viewed from the common terminal; and among the n numberof band pass filters, for a second band pass filter having a pass bandadjacent to the first band pass filter, when f(2) is a center frequencyof a pass band and B(2) is a susceptance value with the center frequencyviewed from the common terminal; the first band pass filter satisfiesone of a configuration (i) and a configuration (ii) for the second bandpass filter as follows: (i) B(2)×{2×f(2)−f(1)}/f(1)<B(1)<B(2) if thefirst band pass filter is the band pass filter at the highest side; and(ii) B(2)<B(1)<B(2)×{2×f(2)−f(1)}/f(1) if the first band pass filter isthe band pass filter at the lowest side.
 2. The wave separator accordingto claim 1, wherein among the n number of band pass filters, for a k-th(2≤k≤n) band pass filter, when f(k) is a center frequency of a passband, and B(k) is a susceptance value with the center frequency viewedfrom the common terminal; the first band pass filter satisfies one of aconfiguration (iii) and a configuration (iv) for each of the second ton-th band pass filters as follows: (iii)B(k)×{2×f(k)−f(1)}/f(1)<B(1)<B(k) if the first band pass filter is theband pass filter at the highest side; and (iv)B(k)<B(1)<B(k)×{2×f(k)−f(1)}/f(1) if the first band pass filter is theband pass filter at the lowest side.
 3. The wave separator according toclaim 1, wherein the first band pass filter is an elastic wave filterincluding a series arm resonator connected to the common terminal. 4.The wave separator according to claim 3, wherein the first band passfilter further includes a parallel arm resonator connected between oneof nodes of the series arm resonator and a reference terminal.
 5. Thewave separator according to claim 1, further comprising: a matchingcircuit connected to the common terminal; wherein the first band passfilter satisfies one of the configuration (i) and the configuration (ii)for the second band pass filter without matching by the matchingcircuit.
 6. The wave separator according to claim 5, wherein thematching circuit includes an inductor including a first end connected tothe common terminal and a second end connected to the referenceterminal; the inductor is embedded in a multilayer substrate; and the nnumber of band pass filters are mounted on the multilayer substrate. 7.The wave separator according to claim 1, wherein the wave separator is amultiplexer.
 8. The wave separator according to claim 1, wherein thewave separator is a quadplexer.
 9. The wave separator according to claim1, further comprising an antenna and an inductor connected to the commonterminal.
 10. The wave separator according to claim 1, wherein each ofthe n number of band pass filters includes surface acoustic wave filtersor bulk acoustic wave filters.
 11. The wave separator according to claim1, wherein each of the n number of band pass filters includes a chipinductor and a chip capacitor.
 12. The wave separator according to claim1, wherein each of the n number of band pass filters includes series armresonators, a parallel arm resonator, and a longitudinally coupledfilter.
 13. The wave separator according to claim 3, wherein the seriesarm resonator is directly connected to the common terminal with noelements interposed therebetween.
 14. The wave separator according toclaim 12, wherein the parallel arm resonator is located between one ofnodes of one of the series arm resonators and a reference terminal. 15.The wave separator according to claim 1, wherein the wave separator is amultiplexer including a matching circuit.
 16. The wave separatoraccording to claim 15, wherein the multiplexer includes a multilayersubstrate including therein the matching circuit.
 17. The wave separatoraccording to claim 16, wherein the n number of band pass filters arepiezoelectric chips mounted on the multilayer substrate.
 18. The waveseparator according to claim 17, further comprising a sealing resinprovided to seal the n number of band pass filters on the multilayersubstrate.
 19. The wave separator according to claim 1, wherein the nnumber of band pass filters are reception side filters that filter areception wave input from the common terminal.
 20. The wave separatoraccording to claim 1, further comprising: a matching circuit connectedto the common terminal; wherein the matching circuit includes aninductor including a first end connected to the common terminal and asecond end connected to ground, and a capacitor connected in seriesbetween an antenna and the common terminal.
 21. The wave separatoraccording to claim 15, wherein the multiplexer is applied to Band2 andBand4.
 22. The wave separator according to claim 15, wherein themultiplexer is applied to Band2, Band4, and Band30.
 23. The waveseparator according to claim 15, wherein the multiplexer is applied toBand1 and Band3.
 24. The wave separator according to claim 15, whereinthe multiplexer is applied to Band1, Band3, and Band1.
 25. The waveseparator according to claim 1, wherein the wave separator is ahexplexer.